The present invention relates to a guide for the sliding element of a push-type electric device such as a pushbutton switch, and more particularly, to such a guide which allows smooth back and forth movement of the sliding element.
FIGS. 1 through 6 of the accompanying drawings illustrate one prior guide for use in a push-type electric device such as a pushbutton switch. The guide has a thin case 1 in the form of a rectangular parallelepiped having an elongate rectangular opening 1a defined in a top wall thereof.
A control member of knob 2 forms the sliding element of the pushbutton switch and is substantially identical in shape to the case 1. The knob 2 is slidable vertically within the case 1 and has a head 2a projecting out of the opening 1a. Fixed terminals 3 project out from the bottom of the case 1. The case 1 houses movable contacts (not shown) which may be brought into contact with fixed contacts connected to the fixed terminals 3 by sliding movement of the knob 2. The knob 2 is normally urged by return spring 4 in a direction toward the top wall of the case 1. When the knob 2 is not depressed, the movable contacts are kept out of contact with the fixed contacts.
The case 1 includes opposite longitudinal walls each having a respective pair of vertical guide grooves 5 in its inner surface for guiding back-and-forth movement of the knob 2, the guide grooves 5 of each pair being spaced from each other and extending vertically in the direction in which the knob 2 is moved.
The knob 2 includes opposite outer side surfaces facing the inner surfaces of the longitudinal walls of the case 1 and each having a pair of ridges, 6 slidably fitted in the guide grooves 5 respectively. Each of the guide grooves 5 has a width larger than the width of a corresponding one of the ridges 6, as can be seen in FIGS. 3 and 5. Such a width difference provides for any dimensional errors of the case 1 and the knob 2 formed during molding, and also prevents sluggish movement of the knob 2 in the case 1, which would otherwise take place if the ridges 6 were fitted too lightly in the guide grooves 5.
Therefore, the knob 2 is disposed in the case with the ridges 6 loosely fitted in respective guide grooves 5. The knob 2 will then smoothly move back and forth while the ridges 6 are guided by the guide grooves 5, for carrying out quick and reliable switching operation.
When the knob 2 of such a switch is depressed on a righthand portion of its head as shown in FIG. 6, the resilient force from the return spring 4 on the knob 2 becomes irregular or uneven, tending to tilt the knob 2 clockwise. At this time, the upper end of the righthand ridge 6 (as shown in FIG. 6) and the lower end of the lefthand slide ridge 6 are urged against side wall surfaces of the respective guide grooves 6. The knob 2 is now depressed in such a tilted condition.
Conversely, when the knob 2 is depressed on a lefthand portion of its head as shown in FIG. 6, the knob 2 is tilted counterclockwise. At this time, the upper end of the lefthand ridge 6 and the lower end of the righthand ridge 6 are held against side wall surfaces of the slide guide grooves 6, and the knob 2 is now depressed in such a tilted condition.
Therefore, the downward movement of the knob 2 is rendered sluggish, and the operator of the knob 2 is rendered sluggish, and the operator is not given a good feel for the operation of the switch, with the result that the switching may not be performed quickly or reliably. Further, the portions of the knob 2 which are pressed against the side wall surfaces of the grooves 6 of the case 1 are spaced apart, which tends to impose an undue moment on the knob 2 and produce increased frictional forces. For the reasons described above, the knob 2 will sometimes get stuck and not move in the case 1.